Recording materials that utilize color formation resulted by reaction of a color-forming compound and a color-developing agent makes it possible to carry out recording in a short time with a relatively simple device without conducting cumbersome treatments such as developing/fixing. Such recording materials are thus widely used for thermal recording papers used for output recording such as for a facsimile and a printer.
On the other hand, there is proposed a so-called rewritable recording material that can form and erase the colored image on a color-forming layer in a thermally reversible manner.
In a rewritable recording material, when temperature of a composition which is initially in a discolored state is raised, color-formation takes place at a particular temperature and the composition evolves into a colored state. When cooled rapidly from the colored state, the composition can be cooled to room temperature while retaining the colored state, which colored state is then fixed. On the other hand, when cooled slowly from the colored state, discoloring occurs in the course of temperature reduction so that a discolored state same as the initial state or a relatively discolored state is formed.
Further, when temperature of the composition fixed at a colored state is raised again, discoloring occurs at temperature lower than the color-formation temperature. When temperature is decreased from the temperature at which such discoloring occurred, the state is reverted to a discolored state same as the initial state. Use as a rewritable recording material is enabled by thus controlling colored and discolored states.
Conventionally, color-developing agents mainly containing a long-chain aliphatic hydrocarbon group has been proposed as a color-developing agent used for a rewritable recording material as mentioned above. Such compounds make it possible to erase an image by formation of an intermolecular interaction caused by the long-chain aliphatic hydrocarbon group (see Patent Documents 1-4, Non-patent Document 1).
Further, as a color-developing agent used for a rewritable recording material, compounds not containing a long-chain aliphatic hydrocarbon group have been proposed (see Patent Documents 5-7). However, rewritable recording materials using these have not yet been established as practical recording materials due to the drawbacks in compatibility of coloring and discoloring properties and in stability with regard to the color optical density or the repeatability.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 8-301838    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 9-295458    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 10-67726    [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2005-1127    [Patent Document 5] Japanese Unexamined Patent Application Publication No. 60-193691    [Patent Document 6] Japanese Unexamined Patent Application Publication No. 61-237684    [Patent Document 7] Japanese Unexamined Patent Application Publication No. 63-173684    [Non-patent Document 1] Ricoh Tech Report, No. 25 (1999)